Weld testing instrument



March 13, 1951 OJC/LLATOR R. S. ROBERTS WELD TESTING INSTRUMENT Filed May 29, 1948 I INVENTOR.

REX S. ROBERTS BY ATTORNEY Patented Mar. 13, 1951 WELD TESTING INSTRUMIEN T Rex S. Roberts, Belmont, Mass., assignor to Transducer Corporation, Boston, Mass., acorporation of Delaware Application May 29, 1948, Serial No. 30,088

6 Claims.

This invention relates to the testing of welds in welded metals by ultrasonic energy.

The welds in welded metals may be faulty due to the lack of continuity between the parent metal and the weld metal, and due to the number and size of slag pockets which may exist within the weld metal. It is desirable to be able to test the quality of welds from one side of the welded metals, as in the case of large pipes, boilers, tanks, and hulls. It is also desirable to be able to make the tests either directly after the welds are made or in the field.

This instrument provides a readily portable and easily operated test instrument for indicating directly the quality of welds of welded metals. In one embodiment of the invention, ultrasonic energy is produced by a piezo-electric crystal and directed into a pocket of water held by a rubber envelope against a welded plate. The resulting wave is impinged againstthe plate at an angle slightly less than the critical angle between the water and the welded metal. The wave length of the energy is made substantially equal to the minimum diameter of troublesome slag pockets which might occur in the welds, so that the wave will move more or lessunimpeded through a good weld. If discontinuity or excessive slag is present, the Wave will be broken up and a considerable part of its energy will be reflected up into the bead of the weld. Another pocket of water is held by a rubber envelope over the weld and the vibrations from the weld are transmitted through the water to a receiving crystal. By comparing the amplitude of the signal received by the receiving crystal'from a weld under test with the amplitude of a signal from a weld of standard quality, the quality of the weld being tested can be determined. Signals from the weld being tested which are stronger than a signal from a weld of standard quality would indicate a defective weld.

An object of the invention is to test the quality of welds in welded metals.

Another and more definite object of the invention is to test the quality of welds in welded metals with supersonic energy.

The invention will now be described with reference to the drawing, which is a diagrammatic View, with portions in section, of a weld-testing instrument embodying this invention.

The steel plates l and l l have been welded together by the butt weld 12. The small, slag pockets l3 are in the weld.

For testing the weld, the rubber envelope I4 is placed against the plates in the welded area. The 1 envelope has the inner tube l5 which is connected to the water-supply bottle IS. The water through the tube I5 is supplied past the splitter ll into the lower ends of the transmitting tube l8 of the envelope, and into the lower end of the receiving tube I9 of the envelope.

The transmitting tube I8 has the metal cylinder 2G therein, the lower end of which terminates short of the lower end of the tube and has its lower wall turned in to form a seat for the piezoelectric crystal 2l which has its lower face in contact with the water column in the lower end of the tube l8. The upper face of the crystal 2| is contacted by the enlarged lower end of the rod 22, the upper end of which is held by the cap 23 on the upper end of the tube 8. The rod 22 holds the crystal in its seat so that it is deformed, but not moved bodilyby the driving energy impressed upon it. The crystal is connected through the rod 22 which contacts its upper face, and through the cylinder 20 which contacts its lower face, to the high-frequency oscillator 3| which may have a frequency. of 1.5 megacycles.

The receiving tube l9 has the metal cylinder 24 therein, with its lower end terminating short of the lower end of the tube, and has its lower wall turned in and forming a seat for the piezoelectric crystal 25 which has its lower face in contact with the column of water in the lower end of the tube IS. The enlarged, lower end of the rod 26 contacts the upper face of the crystal 25, the upper end of the rod being held by the cap 21 on the upper end of the tube IS. The rod 26 prevents displacement of the crystal 25 when it is deformed by vibrations reaching it through water. The amplifier 29 is connected to the meter 39. The crystal 25 is connected through the rod 26 which contacts its upper face, and through the cylinder 24 which contacts its lower face, to the amplifier 29, which, in turn, is connected to the meter 30.

The tube [9 is placed centrally over the weld l2, with its axis perpendicular to the upper surfaces of the plates Ill and H.

The axis of the tube I8 is arranged at the angle 0 to the axis of the tube [9, which angle is, in the embodiment illustrated, about 29". Assuming the velocity of sound through steel plate to be about twice that of sound in water, an angle of 30 would be the critical angle at which reflection would cause a wave generated by the crystal 2| to proceed longitudinally through the plate, but at which little energy would be introduced into the steel. By making the angle slightly less than 30", more energy will be introduced into the plate and will move in the desired direction towards the weld.

A wave length, corresponding to a frequency of 1.5 megacycles, is selected as being roughly equal to the minimum diameter of troublesome slag pockets in the welds and which is estimated to be about ef, and the oscillator 3 l at that frequency causes the Ecrystal t] to introduce, throughthewate'r' column between its lowerface and the plate [0, energy at that frequency which will move through the plate I0 towards the weld l2.

If discontinuity between the weld metal and the metal of the plates H3 and H fiBXiStSyibI'fif excessive slag is present in the weld, the wave will be broken up at the weld and reflected upwardly through the water column 'in :the tube 19 against the lower face of the crystal 25, causing it to vibrate. The resulting electric energy generated by the crystal 25 is amplified by the amplifier "29 and indicated by the meter'fvii.

"Ihe indication "on the'meterresulting from 'a 'vfeldiundertes't would be compared withthat resulting from the testing "of a standardequaiity weld; 'andif the signal from the weld undert'est were stronger than that "from :a good weld, it would indicate the weld under test was'd'efective. The stronger the signal reflected by 'the weld 'under' testthe poorer the weld.

While'asing'le rubber envelope has-been dis- "closed as providing water" columns for boththe transmitting and receiving crystals, separate env elopesywhich-could be of other sound-absorbing material, could paused for each crystal.

While water has been describedas the coupang liquid, other i-nexpensive and' readily 'a'vail lable liquids could be used.

Whileione embodiment er the invention has "been describedfor'the purpose of .illustration, it

should be understood that the invention is "not -'electromechanical receiver; means providing Ea sonic'column for coupling said receiver to the "weld in the plate' at said' one side-thereof; a highfrequency oscillator connected to said transdiicer; and means connected to said r'eceiyer for indicating "the intensity of the energy reflected joy theweld, the axis of the-second-rnentioned {sonic column extending through the 'we'ld prpen'dicular to'the surface ofthe-plate, and the axis of the "first-mentionedsonic --colur'-r'1n being arranged at an angle'slight-l-y less than'thecriti- Vi cal angle at which refraction causestheenergy, generated by" the transducer, to proceed longitu- "dinally'through the plate'towards' the weld.

2. A weld testing instrument comprising a housing adaptd to be placed" against one -side of a welded plate, means; forming two sonic-col- :umnsfin said housing, said columns having corresponding ends terminating at the plate, "said columns having longitudinal axes intersecting on the other side of said surface and forming an acute angle, an electromechanical transducer connected to the other end of one of said columns so as to direct energy along its said axis, a high frequency oscillator connected to said transducer, an electromechanical receiver connected ito'theotherfind of the ot'he'r ofisaid=columns so *as to receive energy reflected "-frofn a weld along its said axis, and means connected to said re- 'ceiver for indicating the intensity of the energy reflected-bya weld, said axis of said one of said icoluinn's ing at an angle to a line perpendicular to the plate which is less than the critical angle "at refraction causes energy generated by thetra-n'sdlicr to proceed longitudinally through the plate towards the weld.

3. 'A weld "testing instrument as claimed in claim 2in which the axis of the said other column is substantially perpendicular to the plate. L-A weld testing -instrument as claimed in claim 2 in which the housing comprises resilient,

vibration absorbing material separating the two columns. I v, 7

'5. A weld testing instrument as claimed in claim 2 in which the said axis of the said other *column substantially perpendicular to the -plate, and in which the housing comprises resilientJ/ibration absorbing material separating the two columns. V

v 6. An instrument ,for'testi ng a weld in a welded plate comprising'mea'ns providing 'a. first Sonic 1 column having a surface atone e'ndforcontacting one side or a plate alongside a weld therein, an electrorriechanical transducera't the iothe'r end of said coluinn, a highfrquency oscillator connected to said transducen'I-mans'providing a' sec- 26nd sonic column having'a 'surfac'eat one end one side "thereof, an electromechanical receiver at the other end or "said second-column, and mean connected to 's aid'receiver f or indicat- ,ing the intensitylof the he'rg y'rfiected by the wel said columns having 'llong'itudinal axes lntrsctm"an-acute angle on the other 4 side of the plate, said 'axis'orgsam first column pangarraagea "atfanangle 'to a '1ine'perpendicu lar to thepilate which is flss'than the critical angle at which refraction c'a'u'ses 'ene'rgy "generated"by the transducer to'proceedllorig'itud'inally through the plate towards the weld.

REK- s. RQBERTS.

REFERENCES crrnp W Thefollowing"referencesiare' of"record in'the file of this patent:

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